International audience ; This study explores the relations between the International Statistical Institute (ISI) and Turkey during the early republican period. It investigates the ISI’s influence in Turkish statistical reform from the mid- to late-1920s through a Belgian expert who led this reform and conducted the Turkish Republic’s first population census. The study proposes to consider the ISI as an international authority and expert space for the negotiation of conventions of quantification, which contributed to the formation of an international statistical system. Focusing on the case of Turkey in the process of modernization and nation-building during the 1920s, it analyses how this international framework structured national quantification policies outside the Western world, and what this meant for state organization and social order.